The present invention relates to a cylinder head for an internal combustion engine for a vehicle such as an automobile, and more particularly relates to such a cylinder head, the construction of which incorporates a coolant passage for cooling a squish area defined between the cylinder head and a cylinder piston, in which the configuration of said coolant passage is improved for improving the cooling effect provided for said squish area.
An internal combustion engine for a vehicle such as an automobile is often liquid cooled, and in such a case the cylinder head thereof is typically formed with various passages for coolant flow, circulation of liquid coolant such as water through which is effective for cooling said cylinder head and also a cylinder block of the engine. Such a coolant passage is typically formed to run around a part of the periphery of the portion of the cylinder head which defines the roof of a combustion chamber thereof. And, in general, it is known that the configuration of such coolant passages in the cylinder head has a great effect upon the mechanical octane value of the internal combustion engine as a whole.
In order to maintain this mechanical octane value of the internal combustion engine at a desirably high level, it is required to construct the coolant passage so that flow of coolant through it effectively cools the portion of the cylinder head which defines the roof of the combustion chamber, and in particular good cooling should be provided to those portions of the combustion chamber roof which define knocking points, such as the end gas area and any squish areas which are defined in the combustion chamber in cooperation with the piston for said combustion chamber, because such an end gas area and such a squish area are particularly likely to become knocking points. Therefore, it is desirable to so arrange the coolant passage as to well cool such a squish area, and in Japanese Patent Application Ser. No. Sho. 58-35221 (1983), which it is not intended hereby to admit as prior art to the present patent application except to the extent otherwise required by applicable law, there is disclosed a cylinder head construction which gives particularly powerful cooling to such a squish area, in order to maintain the mechanical octane value of the internal combustion engine at a desirably high level.
Now, such a coolant passage which cools the squish area is typically a so-called port lower coolant passage which extends between an intake port or an exhaust port formed in the cylinder head and said combustion chamber roof defining portion of said cylinder head. Nowadays, there is a continuing drive for making internal combustion engines as compact as possible, and particularly the space available in the cylinder head is becoming more and more crowded. This is particularly the case for internal combustion engines which are provided with more than two valves for each of their combustion chambers, such as so-called four-valve engines. In the construction of such a cylinder head, the space available for forming bosses for defining cylinder bolt holes, through which are passed the cylinder head bolts which secure the cylinder head to the cylinder block of the internal combustion engine, becomes rather restricted, and a convenient point to locate said cylinder head bolt bosses is at positions along the cylinder head, in the longitudinal direction of the cylinders, between each cylinder and its neighbor. In such a configuration, it becomes difficult to prevent these cylinder head bolt bosses from obstructing either the inlet of such a squish area cooling port lower coolant passage or the outlet thereof, and quite often in fact both said inlet and said outlet of said coolant passage are obstructed. In such a case, the middle portion of said squish area cooling port lower coolant passage, which is the portion actually adjacent to said squish area which cools said squish area, has a substantially larger cross sectional area than do the inlet and outlet of said passage, and this means that a sufficient flow speed for coolant through this middle passage portion is not attained. Further eddies are produced at said middle passage portion, and as a result, the effectiveness of the cooling provided for the squish area tends not to be sufficient. Furthermore, if there is a connecting aperture in this squish area cooling port lower coolant passage which opens to a coolant passage in the cylinder block of the engine, then coolant will flow in through this connecting aperture from said cylinder block into said port lower coolant passage, but the coolant within the cylinder head coolant passage has a strong tendency to flow across in the direction of the alignment of the engine cylinders, and therefore the coolant which has flowed into the cylinder head coolant passage from the connecting aperture also, after impinging upon the lower wall of the cylinder head coolant passage, has a strong tendency to flow laterally and to flow out without the squish area being sufficiently cooled.